An apparatus for producing mono-atomic point source electron beams comprises a tip disposed within a first vacuum chamber with a volume of less than about 1 cubic millimeter and a pressure of less than 10xe2x88x928 Torr and an electrode.
Many analytical devices, such as electron microscopes, utilize a focused beam of electrons to illuminate a substrate. Sources of these electron beams are often contained in the tips of the analytical device.
Electron point sources, which may be utilized in these analytical devices, are well known. These electron point sources, often on the order of the atomic scale and adapted to provide field emission of coherent electron beams, have been described in, e.g., xe2x80x9cCoherent point source electron beamsxe2x80x9d, Hans-Werner Fink, Werner Stocker, and Heinz Schmid, Journal of Vacuum Science and Technology B, Volume 8, Number 6, November/December 1990, pp. 1323-1324, in xe2x80x9cUnraveling nanotubes: field emission from an atomic wire,xe2x80x9d A. G. Rinzler, J. H. Hafner, P. Nikolaev, L. Lou, S. G. Kim, D. Tomanek, P. Nordlander, D. T. Colbert and R. E. Smalley, Science, 269, pp. 1550-1553 (1995), and in xe2x80x9cCarbon nanotubes are coherent electron sourcesxe2x80x9d, Heinz Schmid, Hans-Werner Fink, Applied Physics Letters, Volume 70, Number 20, May 19, 1997, pp. 2679-2680. The first reference discloses a tungsten tip terminated with an atomically perfect pyramid of tungsten atoms as the electron emitter. The second and third references disclose a carbon nanotube as the electron emitter.
By way of further illustration, U.S. Pat. No. 5,654,548 (xe2x80x9cSource for intense coherent electron pulsesxe2x80x9d) discloses how such sources can be used for one type of electron microscopy. The entire disclosure of this United States patents is hereby incorporated by reference into this specification.
Electron beams have been used in constructing microscopes. For example, U.S. Pat. No. 6,005,247 (Electron beam microscope using electron beam patterns) discloses xe2x80x9cAn electron beam microscope includes an electron beam pattern source, a vacuum enclosure, electron optics, a detector and a processor.xe2x80x9d U.S. Pat. No. 6,043,491 (Scanning electron microscope) discloses xe2x80x9cA scanning electron microscope in the present invention, by employing a retarding method and suppressing interferences between an electron beam and secondary electrons or back scattered electrons, makes it possible to obtain a clearer SEM image with a higher resolution.xe2x80x9d The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Field emitted electron beams are also useful in many types of vacuum microelectronic devices, as described in xe2x80x9cVacuum Microelectronics,xe2x80x9d edited by Wei Zhu, (John Wiley and Sons, New York, 2001).
Fabrication of specialized tips used in scanning electron microscopes and atomic force microscopes is well known to those skilled in the arts. For example, U.S. Pat. No. 6,020,677 (Carbon cone and carbon whisker field emitters) discloses xe2x80x9cCarbon cone and carbon whisker field emitters are disclosed. These field emitters find particular usefulness in field emitter cathodes and display panels utilizing said cathodes.xe2x80x9d U.S. Pat. No. 5,393,647 (Method of making superhard tips for micro-probe microscopy and field emission) discloses xe2x80x9cForming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon.xe2x80x9d The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
The prior art sources of atomic point source electron beam emitters typically must be operated at very low pressures, on the order of about 10xe2x88x928 to 10xe2x88x9210 Torr, to protect them from disruptive contamination, chemical degradation, or destructive ion bombardment by residual gas ions. This often requires the use of complicated, expensive, and cumbersome equipment.
It is an object of this invention to provide a device which allows electron beam point sources to be utilized with samples maintained at pressures in a wide range of vacuums from about atmospheric pressure to 10xe2x88x9210 Torr. The mechanically protective ultra high vacuum enclosure of these delicate electron beam point sources in conjunction with the exceptionally good electron-optical qualities of such sources makes possible very small source to target distances, ranging from about 1 centimeter to 10 nanometers. This in turn reduces vacuum requirements needed for practical application of such electron beams, including scanning electron microscopy.
In accordance with this invention, there is provided an apparatus for providing an electron beam, comprised of a vacuum chamber and comprised of a proximal end and a distal end, wherein the distal end comprises electron transparent material, a source of said electron beam disposed within said chamber, and means for focusing said electron beam from said source of electron beam, wherein said vacuum chamber has a volume of less than about 1 cubic millimeter and wherein the vacuum within said vacuum chamber is greater than 10xe2x88x927 Torr. In one embodiment, an electrode is disposed outside of the vacuum chamber.